Atti Soc. tosc. Sci. nat., Mem., Serie B, 107 (2000) pagg. 7-10, tabb 2.
M. M0RI (*), P. SARTOR (**), F. BIAGI (**)
DIET OF ADULT FEMALES OF PARAPENAEUS LONGIROSTRIS (CRUSTACEA, DECAPODA) IN THE NORTHERN TYRRHENIAN SEA
(WESTERN MEDITERRANEAN)
Abstract
-The foregut content analysis of the adult females of the deep water rose shrimp Parapenaeus iongirostris (Lucas, 1846), collected on the epibathyal fishing grounds of the northern Tyrrhenian Sea, indicated a great variety of endobenthic and epibenthic organisms on which this species feed, whereas benthopelagic prey seemed to play a supple mentary role in the diet. Most prey items were slow-moving invertebrates such as crustaceans, molluscs, polychaetes and echinoderms. Organic detritus was found in all the analysed specimens, especially in those caught down 300 m depth.
Key words
-Parapenaeus ion girostris, Feeding, Crustaceans, Western Mediterranean
Riassunto
-Alimentazione difemmine aduite di Parapenaeus longirostris (Crustacea, Decapoda) nel Mar Tirreno Settentrionaie. Nel presente lavoro vengono riportati i risul tati di uno studio sull’alimentazione di femmine del gambe ro rosa Parapenaeus longirostris (Lucas, 1846), raccolte nel le ore di piena luce sui fondi strascicabili epibatiali del Mar Tirreno settentrionale. L’ analisi del contenuto intestinale anteriore ha mostrato che la dieta è basata su organismi appar tenenti alla fauna endobentonica ed epibentonica, mentre le specie bentopelagiche svolgono solo un ruolo accessorio. Le prede sono rappresentate principalmente da crostacei, moflu schi, policheti ed echinodermi. Ii detrito organico è stato rin venuto in tutti gli individui esaminati, specialmente in quel li raccolti a profondità superiori a 300 m.
Parole chiave
-Parapenaeus iongirostris, Alimentazione, Crostacei, Mediterraneo occidentale.
INTRODUCTION
The deep-water rose shrimp Parapenaeus longirostris (Lucas, 1846) is an important nektobenthic organism of the continental slope communities of the northern Tyrrhenian Sea (Biagi et a!., 1989). This species is included among the most important commercial species of this zone, and it is regularly exploited by the trawl fishery (Sartor et al., 1998).
Data on distribution and abundance of P longirostris in the northern Tyrrhenian Sea were given by Mori et al. (1986), while its reproductive biology by De Ranieri et a!. (1986). The female outnumbered the males and reach a larger size (Froglia, 1982; Ardizzone et al., 1990). Considering its abundance in different Mediterranean fishery areas (Hoithuis, 1980) and the protracted spawning and recruitment periods (Tom et
al., 1988; Sobrino and Garcia, 1994), P. longirostris plays an important role in the structure and function ing of the continental slope ecosystem.
The diet of P. longirostris is poorly known: studies about the diet have been carried out off the Majorca Island (MassutI, 1953) and the Morocco coasts (Lagardère, 1972; Burukowsky, 1979). This paper pre sents some preliminary results of a study on the natur al diet of adult females of P. longirostris inhabiting the continental slope of the northern Tyrrhenian Sea (west ern Mediterranean).
MATERIAL AND METHODS
The specimens were collected on the April 1994, by means of bottom trawl, during mid hours of daylight, in an area off the Giglio Isle (northern Tirrhenian Sea, western Mediterranean) in two commercial hauls car ried out at 180-300 m and 320-450 m depth (from 10°20’E 42°29’N; 10°43’E 42°20’N). They were col lected about 48 h later by last fresh trawl discards on the Tyrrhenian fishing grounds, in order to avoid an additional food source for shrimps represented by the material discarded from trawlers, according to Flint and Rabalais (1981). In total, 130 adult females of P. ion girostris (size-range 27-40 mm of carapace length) were collected. Immediately after capture, all shrimps were stored in a box with ice cubes to slow the digestion and to stop the maceration processes by the gastric mill.
After about 8 hours, the shrimps were brought back to the laboratory, where they were kept frozen at -20 °C until they were examined. The observation of the foregut contents were made with a binocular dissecting microscope spreading the contents into a Petri dish. A fullness value was assigned to each foregut: empty or near empty (< 25% full); partially full (25-49%); full (50-74%), and very full ( 75%) (Abelló, 1989).
The diet of penaeids has been described by several works (see Dali et al., 1990), reporting that the material in the stomachs of the shrimps is finely minced and difficult to identify. So, techniques such as weighing the food, measuring the size of prey or reconstructing prey can not be used for P longirostris. Consequently, we have restricted the analysis to the frequency of occurrence (%
F), a parameter that give sufficient information about the relative importance of the prey items in the diet, according to Hyslop (1980) and Williams (1981).
(*) Dipartimento di Studio del Territorio e delle sue Risorse, Università di Genova, C.so Europa 26, 16132 Genova, Italy.
(**) Dipartimento Scienze dell’Uomo e dell’Ambiente, Università di Pisa, Via A. Volta 6, 56126 Pisa, Italy.
8
MORI M., SARTOR P., BIAGI F.RESULTS
About 26% of the foreguts of P longirostris were emp ty or near empty and 74% contained food (28% par tially full, 26% full and 20% very full).
The prey items consisted mostly of external skeletons of bottom organisms always crushed and often in advanced digestion state, so that very rarely it was pos sible to reach the species level in the identification (Tab. 1). In addition, some inorganic material was found.
Prey items belonged to seven major taxa: crustaceans, molluscs, echinoderms, polychaetes, foraminiferans, fishes and hydroids (Tab. 2). Crustaceans dominated both qualitatively and quantitatively; molluscs and echinoderms were for quality the second and third most important food group, respectively. Polychaetes, foraminiferans and organic material were important in terms of frequency of occurrence, but quantitavely resulted of lesser importance. Hydroids and fishes con tributed little to the diet both in terms of frequency of occurrence and quantity of food.
The crustacean food group was dominated by per acarids, mainly represented by mysids (above all Lophogaster lypicus) and amphipods (Lysianassidae).
Food item % F
Crustaceans
Peracarid appendages and other fragments 47,6
Caridean appendages 7,9
Anomuran chelae 3,2
Brachyura appendages and other fragments 7,9
Unidentified Crustaceans 42,9
Molluscs
Bivalve fragments 25,4
Gastropod fragments 22,2
Cephalopod suckers, eyes and tentacles 9,5 Echinoderms
Ophiuroid arms 19
Sea urchin spines and Holoturians spicules 7,9 Annelida
Polychaete hooks, jaws and setae 25,4 Fish bones, otholiths, scales and vertebrae 14,3
Forarniniferans 36,5
Hydrozoan polyps 1,6
Organic detritus 27
Inorganic particles 6,3
Plastic material 3,2
Other crustaceans, but of lesser importance, were ostra cods and juvenile decapods represented mainly by cran gonids (such as Philocheras echinulatus) and pandalid shrimps (Piesionika spp.), followed by anomurans (Anapagurus sp. and Pagurus spp.) and brachyurans (Portunidae). The crustacean remains consisted of approximately 85% of exoskeleton material and only
15% of soft parts.
Molluscs were represented mostly by juvenile bivalves and gastropods, but they consisted principally of shell material respect than soft parts.
The small amount of cephalopods collected from the foregut contents of P. iongirostris were constituted mainly by the sepiolid Sepietta oweniana. The small echinoderms were mainly ophiuroids (Ophiura sp. and Ophyocten abyssicolum and other unidentified species), found as fragments of arms, although sea urchins and holoturoids were also found. Most of annelids were represented by polychaetes belonging to Aphroditidae and Nephytidae.
Fishes were also observed among the preys, but quite rarely (14.3%); most of the remains belonged to small sized species, as evidenced by the size of the vertebrae and other bones and by the size and shape of the oth olits. Foraminifera, above all Globigerinidae, were mainly recorded in foreguts containing small amounts of food, and they were always present with a scarce number of individuals.
The organic detritus, mostly as unidentified debris, was found with a relatively high percentage of occur rence, but in a low amounts and quantitatively it appeared to increase in the specimens caught in the haul down 300 m depth. Also inorganic and plastic particles were found mostly in the specimens caught in the deepest area.
Tab. 2
-Diet of the adult females of Parapenaeus longirostris.
Tab. 1
-List of the taxa found in the P. longirostris foreguts.
HYDROZOA FORAMINIFERA
Globigermidae POLYCHAETA
Aphroditidae Nephtydae MOLLUSCA
Bivalvia Gastropoda Cephalopoda
Sepietta oweniana (Orbigny) CRUSTACEA
Ostracoda Mysidacea
Lophogaster typicus Sars Amphipoda
Lysianassidae Decapoda
Philocheras echinulatus (Sars) Plesionika spp.
Anapagurus sp.
Pagurus spp.
Portunidae ECHINODERMATA
Ophiuroidea
Ophiura sp.
Ophyocten abyssicolum Marenzeller Holoturoidea
Echinoidea
PISCES
DIET OF ADULT
FEMALESOF
PARAPENAEUS LONGIROSTRIS(CRUSTACEA, DECAPODA) 9
DISCUSSION
The results of the study of the diet show the great vari ety of organisms on which P longirostris feed, mainly crustaceans (amphipods and mysidaceans), molluscs, annelids and echinoderms, and that most of the prey items are slow-moving species. The major food groups found in this study were similar to those identified by Lagardère (1972) in specimens of P longirostris com ing from Morocco. The only differences refer to foraminiferans and ophiuroids, found by this Author in higher and lower number, respectively; this is probably due to the different distribution pattern of these taxa in the two different study areas. Moreover, Lagardère (1972) reported a minimum of feeding activity at the beginning and at the end of the night. The diet of P ion girostris caught off the Majorca Island is constitut ed mainly of decapods, fragments of the brachiopod Griphus vitreus, organic material and mud (Massuti, 1953).
Studies on the natural diet of various penaeids species report that the main component of the their diets were crustaceans, followed by molluscs, polychaetes and echinoderms (Lagardere, 1972; Chong and Sasekumar, 1981; Luna-Marte, 1982; Wassenberg and Hill, 1987;
Dali et al., 1990). Also in captivity some penaeids, e.g.
Penaeus vannamei, prefer to consume little crustaceans (Ogle and Beaugez, 1991).
The important role of amphipods and mysids as food resource is reported also for the diet of gadiform fish es, especially the juveniles, inhabiting the continental slope and shelf of the same area (Sartor, 1995). The feeding on bivalves, gastropods and ophiuroids, organ isms with high calcium content, may represent an important source for the moulting individuals and might facilitate the action of the gastric mill (Suthers,
1984).
In the decapods the digestion process takes place rapid ly, with food being retained in the stomach for only a few hours (Roe, 1984); however, preys containing mostly hard parts may be retained for much longer time than those constituted principally of fleshy tissues (Wassenberg and Hill, 1987). Thus, the apparent impor tance of particular prey groups in the diet (e.g.
cephalopods and annelids) will be underestimated, as noted by Sardá and Valladares (1990).
The organic detritus generally consisted of macerated bodies of different animals, e.g. crustaceans, molluscs, polychaetes and fish. This material may come also from the bottom sediment, representing a substrate for micro-organisms like bacteria, fungi and protozoans (Watling, 1989). Chong and Sasekumar (1981) found that the use of organic detritus as a food source result ed important for Penaeus inerguiensis when it assumes the benthic habits.
The finding of bigger quantity of organic detritus in the specimens caught down 300 m, may be related to a reduction of the feeding activity or to a change of the diet with the depth. In agreement with this hypothesis, Lagardere (1972) reported a reduction of the feeding activity in the oldest specimens that live mostly at the highest depth.
In conclusion, the results of this preliminary study show that P longirostris seem to be an important oppor tunistic predator in the continental slope communities of the Tyrrhenian Sea. However, further studies to examine the nychtemeral feeding rhythms and to deter mine the trophic strategies as a function of changes in the available resources according to depth and season, are necessary.
ACKNOWLEDGEMENTS
We wish to thank the crew of the trawler <<Francesco Padre>> for its co-operation during the work at sea. The individuals were collected during the research program <<Nemed>> funded by CEE (Contract no MED/92/008).
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